Nitrogen mobility in Nd2 Fe17 Nx (x=2.6, 4.5) investigated by magnetic aftereffect

We have used the technique of magnetic aftereffect (MAE) to investigate the mobility of nitrogen (N) in samples of nominal composition Nd2 Fe17 N2.6 and Nd2 Fe17 N4.5. It was possible to detect a thermally activated MAE maximum around 225 K for Nd2 Fe17 N2.6 and 237 K for Nd2 Fe17 N4.5, with and average activation enthalpy of 0.64 and 0.73 eV, respectively. These values correspond to the lower limit in the range of activation enthalpies of diffusion found by several other methods. The differences in the enthalpy spectra obtained by the MAE technique clearly indicate the existence of some structural differences between both samples, although the mechanism of mobility seems to be the same for both concentrations. These results will be compared to former investigations on hydrogen in S M2 Fe17 using the same technique. (author)